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\f0\b\fs24 \cf2 Oceans Give the Most Powerful Evidence Climate of Global Warming
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by Sabrina Shankman and Paul Horn\
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\cf2 Oct. 3, 2017 \'96 Earth's temperature is rising, and it isn't just in the air around us. More than 90% of the excess heat trapped by greenhouse gas (GHG) emissions has been absorbed into the oceans that cover 2/3 of the planet's surface. Their temperature is rising, too; it tells a story of how humans are changing the planet.\
This accrued heat is "really the memory of past climate change," said Kevin Trenberth, the head of climate analysis at the National Center for Atmospheric Research and co-author of a\'a0new paper on ocean warming.\
It's not just the amount of warming that is significant\'97it's also the pace. The rate at which the oceans are heating up has\'a0nearly doubled since 1992. That heat is reaching ever deeper waters, according to a recent study. At the same time, concentrations of CO
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\fs24 \cf2 in the atmosphere have been rising.\
The charts that follow [see original URL] show how the oceans are changing and what they're telling us as a thermometer of global warming.\
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\i \cf2 Oceans Storing More Heat as
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\i\fs24 \cf2 Builds Up\
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\i0 \cf2 The oceans have absorbed 90% of the extra heat trapped by increasing GHGs. During 2015-2016, the amount of heat stored in the upper 2,000 meters of the oceans reached its highest point on record.\
Scientists say the accumulation of heat in the oceans is the strongest evidence of how fast Earth is warming due to heat-trapping gases released by the burning of fossil fuels.\
Oceans have enormous capacity to hold heat. So ocean temperatures, unlike temperatures on land, are slow to fluctuate from natural forces, such as El Ni\'f1o/La Ni\'f1a patterns or volcanic eruptions. Think night and day, said Trenberth. As night falls on land, so do air temperatures. But in the oceans, temperatures vary little.\
This makes it easier to tease out the influence of human-caused climate change from other possible causes of surging ocean heat.\
How much extra heat are we talking about? And what are the impacts on the climate system? "On a day-to-day a basis, it's really quite small," Trenberth said, but the cumulative effects are not.\
According to research by Trenberth and Lijing Cheng, of the Institute for Atmospheric Physics in Beijing, the heat storage in the oceans during 2015 and 2016 amounted to a stunning force: an increase of 30.4 X 10
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\fs24 \up0 \'a0joules of energy roiling Earth's systems since 1960. The overload is helping throw off Earth's energy balance, needed for the climate to be relatively stable. Put another way: The excess energy amassed in the oceans since 1992 is roughly equivalent to 2,000 times U.S. electricity generation during the past decade, the researchers explained. And a 3rd way: It is many times all the energy humans have ever used cumulatively.\
Ocean surface temperatures have been rising about\'a00.12\'b0C per decade on average over the past 50 years. The higher temperatures are driving marine life toward the poles in search of livable habitats, bleaching coral reefs, and causing severe impacts on fisheries and aquacultures. They also contribute to more frequent and intense extreme weather events. In the 3 back-to-back deadly hurricanes of 2017\'97Harvey, Irma and Maria\'97warmer waters played a role\'a0in worsening the storms.\
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\i \cf2 Ocean Temperatures: Warm and Warmer\
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\i0 \cf2 Scientists who take the oceans\'92 temperature have documented warmer-than-average waters in recent years, as Earth accumulates more heat from the rise in GHG emissions. These maps reveal far more red (areas with temperatures above the historical record going back to 1880) than blues during 2015, 2016 and through August 2017. The areas below that average cover less than 1% of Earth\'92s surface: patches of ocean just south of Greenland and a smaller one just north of the Antarctic Peninsula.\
Though ocean temperature represents a clear signal of climate change, one challenge for researchers is that the record only goes back so far. Since the early 2000s, an international effort called Argo has launched nearly 4,000 ocean-going sensors that gather important data about the oceans, including temperature.\
Meanwhile, as oceans heat up, thermal expansion causes sea levels that are already rising from the melting of land ice (triggered by higher air and sea temperatures) to rise even more. Nearly 50% of the sea level rise so far has come from ocean warming, according to new work by Cheng and Trenberth. Much of the rest comes from the melting of ice on Antarctica and Greenland.\
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\i \cf2 Oceans Warm and Expand \'96 and the Seas Rise\
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\i0 \cf2 The increase in ocean heat causes seawater to expand, raising sea level. In 2015, roughly half of global sea level rise was caused by ocean warming.\
Ocean warming can impact sea level rise in another way, too. This year has seen\'a0extensive losses from Antarctica's ice shelves. "It's most likely because that ice is being undermined through warmer ocean underneath the ice, which is contributing to the thinning of the ice and weakening of the shelf," Trenberth said. The ice shelves themselves are already floating. But they are attached to land and play a critical role in slowing the ocean-bound ice flow from the massive ice sheets behind them. Scientists say the West Antarctic Ice Sheet alone holds enough ice to raise global sea level by about\'a011 feet and Greenland holds twice that much.\
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\cf2 insideclimatenews.org/news/03102017/infographic-ocean-heat-powerful-climate-change-evidence-global-warming}